Aluminum CNC Machining: Alloy, Tolerance, and Setup Choices

Most of our aluminum CNC machining work lands on 6061-T6. It machines cleanly, welds, anodizes well, and holds tight tolerances without much fuss. If your part is a bracket, a housing, a manifold, or a fixture plate, start here. Yield strength sits around 276 MPa, which is enough for most structural work that is not seeing continuous load.

When weight matters more than strength, 7075-T6 is the next step. It cuts at roughly 503 MPa yield but costs more and is harder on tooling. Chips break shorter and the surface can tear if feeds are too light. Use it for aircraft fittings, high-load brackets, or anything where a thinner wall has to survive vibration.

For parts that need corrosion resistance or will be anodized a specific color, 5052 and 5083 are common. They are softer, gummy at low speeds, and not ideal for thin walls. 2024-T4 machines well but has poor corrosion resistance unless it is coated or clad. 6063 is for extrusion-like profiles where finish matters more than strength. ADC12 is die-casting grade, not for machining from billet.

If you are unsure, send the drawing. We match the alloy to the load case, the finish, and the quantity. A 6061 part that is over-engineered is cheaper than a 7075 part that is not needed.

• 1
  6061-T6General purpose, good finish, easy to anodize.
• 2
  7075-T6High strength, tighter tool control needed.
• 3
  5052 / 5083Corrosion resistance, softer, gummy at low speed.
• 4
  2024-T4Good machinability, needs coating for corrosion.

We hold ±0.005 mm on features that need it. That is not a default. A general machining tolerance of ±0.1 mm keeps cost down and is fine for most clearance holes and outer profiles. Reserve the tight callouts for bearing bores, mating faces, and dowel pin holes. Every tight feature adds inspection time and often a second setup.

Surface finish follows the same logic. As-machined aluminum sits at Ra 1.6–3.2 μm. A high-finish cut gets you Ra 0.8–1.6 μm, and fine finishing can reach Ra 0.2–0.8 μm on flat faces and bores. If the print calls for Ra 0.4 μm across a deep pocket, expect us to ask about tool reach and whether the surface can be reached at all.

Thin walls are the other limit. A 0.5 mm wall in 6061 is doable at low depth of cut, but it will deflect. Chatter shows up as a rippled finish. If your design needs 0.3 mm walls over a long span, we will likely suggest a different alloy or a redesign. Aluminum moves under cutting force more than steel does.

A part belongs on a 3-axis mill when all features can be reached from one direction, or when the part can be flipped once and located off a flat face. Simple plates, covers, and brackets fall here. Three-axis work is the cheapest per part and the fastest to set up. We run 27 three-axis machines for this kind of work.

Four-axis suits parts with features on multiple faces around a single axis. Think of a shaft with cross holes, or a housing with ports on four sides. A rotary table lets us index without re-fixturing. That saves the location error that comes from flipping a part by hand. We have 12 four-axis mills and a Ø400 mm rotary table.

Five-axis is for contoured surfaces, deep pockets with undercuts, and parts that need one setup for tight positional accuracy. Impellers, turbine blades, and complex medical housings live here. Simultaneous five-axis also lets us use shorter tools, which reduces chatter on deep cavities. We run 16 simultaneous five-axis centers. The setup cost is higher, so it pays off when the geometry demands it or when volume justifies the fixture.

The wrong choice costs money both ways. Putting a simple plate on a five-axis center wastes setup time. Putting a contoured part on a 3-axis mill means multiple fixtures and stacked tolerance. Send the model and we will tell you which one it is.

We quote and return a free DFM analysis within 12 hours. That analysis flags thin walls, tool reach problems, and tolerances that will drive cost. Production can start within 24 hours of a released order. Parts ship in 3–5 days for most aluminum work. Historical late-delivery probability sits below 2%.

There is no minimum order quantity. One prototype and a 10,000-part run go through the same first-article process. Raw material is checked on arrival, in-process dimensions are monitored, and every part gets a final inspection before it leaves. Reports are available on request.

Finishes include anodizing in clear, color, hardcoat, and conductive types; electroless nickel, zinc, silver, and gold plating; powder coating and black oxide; bead blasting, tumbling, brushing, and polishing. Laser marking is available down to 1.5 mm character height. If your part needs a masked anodize or a specific Ra on one face only, say so on the print.

We hold ISO 9001:2015, IATF 16949:2016, ISO 13485:2016, and ISO 27001:2022. That covers quality management, automotive, medical device, and information security. Uploads are secure and confidential, and an NDA is available on request.